Multicasting, e.g., IP multicasting is widely used as a method to send transmissions to a select group of recipients that belong to what is called a “multicast group.” Multicast allows a single stream of packets, e.g., media stream packets to be sent a plurality of recipients, e.g., client devices that are in the same multicast group. Wireless networks, however, pose new situations that multicast, as originally conceived, was not meant to address.
In an infrastructure wireless local area network (WLAN), client devices (“clients”) are associated with an access point (AP) that is typically directly coupled to a wired network. Recently, access points whose access point functionality is controlled by a controller—so called lightweight access points—have become widely used. Clients that are members of the same multicast group might roam across many controllers, e.g., from one access point controlled by one controller to another access point controlled by another controller. To successfully multicast, in multicast strategy, multicast information in the form of one or more packets is flooded to every access point on every controller. If a single client, for example, roams across four access points, each having a different controller, each time sending the appropriate “join” request to move to the access point, then every access point of each such controller would need to broadcast multicast packets whether or not a client of the particular multicast group is associated.
Similarly, a controller can and does forward multicast traffic from the wired network where no clients that are members have joined. This could be routing protocol updates or multicast groups that the wired network is flooding toward the WLAN controller interface. Thus, there would clearly be an advantage in a wireless network to have processes that keep track of roaming clients that are meant to be receiving multicast traffic, and to avoid sending traffic to access points that have no recipients, e.g., client devices associated.